Frequency modulation detection



N H. E. 'GOLDSTINE 2,334,190

FREQUENCY MODULATION DETECTION File d June 18, 1940 OUTPUT g lNVENTOR HALL/1N E. GOLDST/IVE k a W N 4 q LLI 5 v ATTORN EY Patented Nov. 16, 1943 2,334,190 TFREQilENCYTMODULATION DETECTION Hallan E. Goldstinaltocky Point; N; Y; assignor 1t0i Radio: Corporation of America, a corporation Application June 18, 1940; Serial No.'341,111

' 8@Claims. (01150- 27) "This application concerns a new and I improyed" modulation monitor, The modulation monitor of this disclosure maybe used with'any' type'of frequency modulator monitorfdescribe'd was used with a 5'00'm'c'. tele"- visionrelay; the monitor 01 my' invention, I take a small amount of energy from the output of the termina-rtransmitter'or one "of the relay stations and convert output to amplitude the frequency modulated modulation and then amplifythe' video signal so" that it may b'e applied' to a coaxial cable for monitoring the output of the station at a'conveni'ent place} I In describing myinvention, referencewill be made to the attached drawing wherein-the sin gle figure illustrates an embodiment" of my monitoring system.

In order 'to monitor is desirable that the monitor be simple'incom' struction' andasfree as possible ofelements which would introduce'undesirable distortion. The frequency modulation detectors'of the monitor consi'st' of two concentric line 'resonatorswhich are essentially a quarterwave l'ength l'ong. "These two resonators" are designated generally by the reference numerals Z and 4" an inner conductor 6 and 8" and an'outer conduct'or which is at ground potential. "In this particularcase, the inner conductors '6' and f8 weremade of Invar, This material was used"be'-' causeit has a rel'atively high loss and it was rigid and relatively desired that the circuit be free from temperature effects andyet have "a rel'ativelylow Q so that the frequency band, of at least'i5 me. 'could be easily handled. The Qf o'f'these' circuits was about 40; "An advantage of using a line section for the discriminators although the particular the ideo transmission or other frequency modulations "on waveenergy,it

andeach comprise is that the circuits-are rigid and prevent vibration from producing an undesired output from micro-' phonics; r I

The input to thise circuits is supplied from the transmitter by radiation" or by" coupling and may be taken from the antenna orthe transmis'- sionline leading to the-antenna and isappliedat ill-in such-a manner that the'energy which the monitors require does" not appreciably affeet thetransmissionline; The-input to the-fre quency discriminator-circuits 6 and 8 is made effectively aperiodic over the band which it is desired todetect so that if a transmission line, anumberof wave lengths long, isused t'o feed" these diodes; it: is necessary that this transmission line should be terminated in its character istic impedance'iandz the: capacity which: the line l 26 and condensers cathodes- 60= works into is tuned out byflinearis' or inductor 2% so that the line wouldib'e substantially f-la t-airirl would not changethe frequency characteristic of the circuits 6 and 8 over the frequency handthrough which the carrier frequency is shifted' The small tuning inductance 26' which is" used parallel with the load resistor 21)" to tune; outthe' capacity to ground of the input circuit may he as illustrated of thepo or cylinder or line type; although other typesmay be used.

The transmission line then ita'lresfenergy from the transmitter andsup'plies it to aresistance termination in the line. I This resistance is shown at 20. This voltage is fed-by means of two small condensers 30 and 36 to a high impedance point on the Invar lines 6 and 8. These'condensers are adjustable and areset so that the coupling of the'lines will be quite small and, also," to bal an'celthe'voltage of the two circuits. These circuits" comprising lines 2 and- 4, tuning inductance 30' and are thentuned an equal amount off of resonanceyone above and thecther below the frequency of themo'dul'ated wave the modulations onflwhich are to be-inves-'- ti'gated'. i

Preferably; the resonant frequencies of the lines '2' and 4 are subject to' a 'commoncontrol means. Forexample; I proposeto' use a mechanca'l linkage, illustrated sch'emati'ca-llyat T, a'ctu ated by a'single control 9' to change the'resonant frequency of both of the resonant control" lines simultaneously; This change is accomplished by adjusting the length of the innermembers' 8' and 8' by means or threadedmemberst" and 8;, 113-; dividual adjustment of the lines by thisine'ans or additional means'p'rovides for tuning each in below frequency; 'By this means I ami'enabl'ed to set the peak of the resonant frequencies of the two diode-systems afixed frequency apart, say 10 m'c;, and yet I- am able to shift the center frequency maintaining this fixed separation, us, if the carrier fre quency changes slightly, it is only necessary to operate the common control which shifts the frequency of both of the lines in the samedire'ction like amounts.

A frequency diode rectifier system40 the plate 44* of WhichisvtalJDed-about halfway" up the line 6; rectifies the voltage and converts it to' amplitude modulation; A similar diodesystem 48 the plate 50* of which: is coupled tothe line 8, rectifiesvoltages in the line 4} The and 64: ofthese diodes 4-U and- 48 then feed through resistances' -fls and 88' t'dth'e input or: a push-pull video a "plifier. Thi's am i then feeds voltage to the grid plifier comprises tubes 10 and 12 having control grids l4 and 16 coupled by condenser 18 and 80 to the resistances 66 and 68. Acorn type tubes 10 and 12 are used for the input tubes of the video amplifier so that the diodes 40 and 48 will work into a low capacity. An extra amplifier stage comprising tube 90 having its grid 94 coupled by condenser 96 to the anode 98. of'tube "is used in one side. of the amplifier to invert the phase of the voltages and then the outputs derived from 12 are combined in w W plate circuits ina common resistor 1M which I06 of tube'loo of another stage of single ended amplifier. single ended amplifier has an anode H0 coupled by condenser H2 to the grid Ji l of an additional amplifier stage tube H6. It is necessary that the phase shift be kept very' low in the additionalorinverting stage of the video amplifier so thatatithe higher frequencies the two sides of the amplifier will add properly in phase. I

-.The output of the amplifier H6 is fed from the cathode circuit resistance no so that it may be possible to work into a coaxial cable and terminatev this cable in its characteristic impedance. A kinescope monitor or oscilloscope may then be used to'determine if the signal is being transmitted through the relay station pro-perly. The output here is shown as being derived froma jack IZAcOupled-by a twisted pair to the cathode of tube H6. h

. 'Ifhe amplifier is fed from a regulated power supply not shown. I An additionaladvantage accruing from the use of mysystern is that amplitude, variations are in push-push on the amplifier stages Til. and'l2 as well as on the rectifierstages it and 48 and are more completely cancelled out. 7

It will be noted that the outputs of the two dioderectifiers, oi the off-tuned or opposed slope frequency modulating converting system, are kept. separate and are separately amplified and then supplied to a common circuit in the outputs of amplifiers 9i? and 'l'Zfin phase to combine the same. In systems of his general nature known heretofore and used, say for Wave demodulation and/or automatic'frequenc'y control purposes, the rectifier outputs have been added and the difference of the differentially combined outputs used. In theseknown systems the cathode of one of the rectifiers is at high radio 'f-requency potential and introduces many problems such as insulation, etc.,

not encountered in my 'systerni 1The use of the separate push-pullexcite'd amplifiers. Ti] and 12 working into a common output circuit ltd byway of 'an unequal number of'amplifier stages in the two paths permits use of the diodes as illustrated with both cathodes at low-frequency potential. When the output of one diode, say diode it, is switched by means of switches HI and l33,"from the input of the reverser tube to theinput of the nexttube Bil so that the outputs of the diodes are connected for push-push operation, amplitude modulation may be detected.- That is, dueto the effective push-push output of the rectifiersamplitude modulation present on the transmitter will be detected. This might be useful in checking or adjusting for amp 'tude modulation output. There are several modifications which mig ht be desirable to use in connectionwith this monitor amplifier. One is that thediode outputs of the converter circuit may be used tosupplyyaf;

2,334,190 P f J the anode l00 of amplifierQll and the anode I02 of amplifier the common portion-of .their a This voltage for automatic frequency control so that if the frequency changes, the direct current from the diodes will be unbalanced and will operate a tuning mechanism to correct this unbalance. High impedance quarter wave length lines I30 and I32 open at the far end may be connected to the cathodes of the diodes to suppress the radio frequency Without adding materially to the capacity which the diodes have to work into.

What is claimed is:

1. In a modulated wave analyzing circuit, two

-. frequency discrimination circuits having overlapping conversion characteristics, means for impressing the'waves to be analyzed on said circuits, a pair of detectors each having a cathode :and an additional electrode, a circuit coupling the additional electrode of each detector to one of said frequency. discrimination circuits, a modulation' potential impedance coupling the cathode of each detector to ground, an output circuit, a firstamplifier comprising an odd number of tubel'stages coupling one of me an even number of tube stages coupling the otherof' said impedances to said. output circuit and a switch for removing a stage from one of said am'plifiers. I

2. In a system for detecting changes in fre- I quency of wave energy, two circuits one of which is tuned to resonance above the mean frequency of the wave energy and the other of which tuned to resonance below the mean'frequency of tential and at low wave energy frequency potene tial, an output circuit, a first amplifier comprising an odd number of stages coupling the oath- ,ode of one detector to said output circuit, and.

a second amplifier comprising an even number of stagescoupling the cathode of the other detector to said output circuit.

' 3, In means for detecting variations in the frequency of wave energy,

quency of the wave energy, two means for con ve'rting variations in the frequency of said wave energyinto corresponding variations .in the am plitudeofsaid wav energy, a rectifier coupled to each of said means, a separate output circuit for each rectifier, a combining circuit, a first amplifier comprising an odd number of amplifier tube stages coupling the output circuit of one of saidrectifiers to said combining circuit, and

asecond amplifier comprising an even number 7 of amplifier tube stages, coupling the output oncuit of, theotherxof said rectifiers to said come.

bim'ng; circuit..

q 5;1In Lmeans; for detecting variations in the.

c said impedancesto said output circuit, a second amplifier compris a pair ofcircuits resonant above and below respectively the mean fre- 'odd number of amplifier frequency of wave energy, apair of resonant lines, resonant above and below respectively the mean frequency of the waves to be detected, a rectifier system coupled to each line, a separate output circuit for each rectifier system,- a com+ bining circuit, a first amplifier comprising an tube stages coupling the output circuit of one of said rectifier systems to said combining circuit, and a second amplifier comprising an' even number of amplifier tubestages coupling the output circuit of the other of i said rectifiersystems to said combining circuit.

6. In'means 'for' detecting variations in, amplitude or in frequency of wave energy, a pair of resonant circuits, resonant above and below're- .15 spectively the mean frequency of the waves to be detected, a rectifier system coupledto each of said circuits, a separate output circuit for each rectifier system, a combiningcircuit, a first amplifier comprising an odd number of amplifier '20 tube stages coupling the, output circuit ofone Q of said rectifier systems to said combining cir--. cuit, a second amplifier comprising an even number of amplifier tube stages coupling the output circuit of the other of saidrectifier sys-' tems to saidcombining, circuit, and means for removing an amplifying stage from one of said amplifiers or adding an amplifier stage to one of said amplifiers whereby said amplifiers both have an odd number of stages or an even number of stages.

7. In a system for demodulating'wave energy the wave length or the amplitude ofwhich may vary, separate means excited by said wave energy for producing two wave energies, the amplitudes of which vary in accordance with the variations in wave length of said first wave energy and each of said devices and ground or potential, a combining, circuit, an amplifier insecond amplifier and ances and between the output of said second amof said first wave output, a separate each rectifier to said output, there being a like number of tube amplifiers in said amplifier systems when said wave energy is of varying amplitude and an unlike'number of amplifier tubes in said amplifier systems when said wave energy is of varying wave length.

8. Ina system for demodulating wave length modulated wave energy, a pair of' electrondischarge devices eachhaving an anode and a cathode, a pair of circuits tuned, one to a frequency above the mean frequency of said wave energy and the other to a frequency below the mean frequencyot-said wave energy, said circuits being responsive to said wave energy, a coupling between theanode and cathode of one of said devices and, one of said circuits, a. coupling between the anode and cathode of the other of sa'idfdevices and the other of said circuits, an impedance connected between the cathode of eluding an even number of discharge tubes connected in cascade, means coupling the input of said amplifier to one of said impedances and the output of said one of said amplifiers to said combining circuit, a second odd-number-of-stages amplifier comprising at least one electron dis chargeltube, a coupling between the input of said .the other of said imped plifier and said combining circuit.

HALLAN GOLDS'II'INE;

. also'in accordance with the amplitude variations energy, rectifier coupled to each of'said means, an electron discharge tube amplifier system coupling equivalent 

